In order to reduce the density of a sheet molding compound (SMC) or bulk molding compound (BMC), high-density inorganic fillers, such as calcium carbonate, are removed from the formulation and replaced with thermoplastic in an effort to maintain surface quality characteristics. Another approach common to the field is to remove a portion of the inorganic filler and replace some of the inorganic filler with the industry standard SMC-1 hollow glass microspheres. Spherical particulate under processing conditions have a tendency to become displaced from the molding compound matrix. Additionally, under the stresses associated with sanding a molded article, such hollow glass spheres have a tendency to rupture, leaving a cavity in the molded article that is amenable to disintegration. The ruptured hollow glass sphere is manifest in a painted article as a paint pop that effectively destroys the surface finish. Due to these problems, hollow glass spheres have not been acceptable in SMC or BMC molded articles requiring a class “A” surface finish as defined by Powder Prime Patent. As class “A” surfaces are routinely required in vehicle components, the ability to form a low density class “A” SMC article would lower the vehicle weight and thereby increase fuel efficiency.
Thus, there exists a need for a low-density class “A” SMC or BMC containing hollow glass microspheres that retains class “A” surface finish characteristics.